The present invention relates to temperature-sensing apparatus and, more particularly, to a novel improved temperature-to-frequency conversion apparatus.
It is known to provide apparatus for conversion of a sensed parameter, such as temperature, to a periodic signal having a frequency related to the parameter magnitude. For example, it is often desirable to provide apparatus for conversion of sensed temperature to a signal frequency, with the signal frequency being counted and displayed, as on the display apparatus of a clock, or clock radio, in which the temperature-sensing apparatus is installed. Prior art sensed-parameter-to-frequency conversion circuitry has been generally characterized by a non-linear relationship of output frequency with respect to the magnitude of the sensed parameter. Further, relatively large amounts of electromagnetic interference are typically generated by the relatively narrow (i.e. low duty cycle) output frequency pulses of prior art conversion circuits, which electromagnetic interference is particularly deleterious to proper operation of the radio receiver section of a clock radio. Additionally, many prior art circuits require that, because of tolerance variations in components (e.g. timing capacitors and the like) and supply voltage, that the circuit include some form of trimmable control element which allows compensation for the circuit-to-circuit variations, but which compensation element itself introduces additional non-linearities in the relationship of output frequency to sensed parameter magnitude. Improved apparatus for conversion of a sensed parameter to an output waveform frequency, overcoming the above-described shortcomings, and in a low cost manner, is therefore highly desirable.